Denso iridium racing spark plugs feature a special hardened insulator that is 20% stronger for hard core racing applications. Surface gap plug with iridium center electrode for increased longevity. Patented self-cleaning electrode design. Silicone oil coated insulator to repel moisture and carbon buildup. Handles extreme compression and boost levels. Machine rolled threads prevent seizing or cross threading during installation and removal. 100% pre-fired to assure the highest quality possible. Purified alumina powder insulator provides exceptional strength and thermal conductivity. Five rib insulator prevents flashover. Copper-glass seal bonds center electrode and insulator for a gas-tight seal.